1. Field of the Invention
The invention relates to biological treatment of waste through activated sludge and fixed film processes.
2. Description of the Prior Art
Biological treatment of waste often employs either activated sludge or fixed film. Activated sludge is the semi-liquid biomass removed from the liquid flow of waste, particularly from the liquid flow of wastewater. Before it is fully decomposed by aerobic microbial decomposition, activated sludge is put into aeration tanks to facilitate and further undergo aerobic microbial decomposition. Fixed film processes use biological aerators that rotate around a central horizontal shaft, which is submerged in the wastewater. As the aerators reemerge from the surface of the wastewater, they catch air in specially profiled cells.
A typical activated sludge or fixed film apparatus uses an aeration tank, also referred to as an aeration basin or biotank, and a separate settling tank or gravity clarifier, also referred to as a settling tank or gravity separator. See, for example, U.S. Pat. No. 6,039,873, to Stahler, the entire disclosure of which is herein incorporated by reference. The purpose of the clarifier is to remove the suspended solid particles in the wastewater. The solid particles range in size from microscopically fine to rather coarse, and consist primarily of undissolved or unoxidized material, spent bacteria and other microorganisms. The clarifier can be one of a number of types, including circular, hopper bottom or rectangular. In the prior art, however, they are all separate from the aeration tank.
Once separated from the supernatant liquor, the solid particles settle to the bottom of the clarifier to form a sludge. The sludge is then returned to the aeration basin by a return sludge pump. The sludge, which contains viable bacteria and other microorganisms, reacts with the wastewater in the aeration basin to further the activated sludge process. The rate of return can vary widely in proportion to the rate of influent flow. Typical rates are 25-100 percent of the influent flow.
The prior art systems work reasonably well, but most use either a fixed film process or an activated sludge process, thereby foregoing the advantages of the other process. Specifically, the fixed film process is simpler, and provides more stable treatment with lower power costs, while activated sludge is more flexible and meets higher quality effluent standards.
Furthermore, in the prior art the separation of the clarifier from the aeration tank creates a need for return pumps and piping that considerably increases construction cost and complicates operation. Finally, the prior art mounting of the rotating contact aerators in the aeration tank also increases construction cost and operation complexity. It is well known to construct concrete or steel supports or haunches to mount the bearings of contact aerators. The bearings are then bolted to the steel brackets or concrete haunches. When a rotating contact aerator must be removed from the aeration tank, however, it must first be drained so that the mounting bolts are accessible. Accordingly, flow through the plant must be stopped and the mixed liquor inside the aeration tank removed by pumping or hauling.
The present invention comprises a waste treatment apparatus and method. The apparatus includes an aeration basin (e.g., an aeration tank or bio-tank), an aerating device (e.g., a fixed film aerator or rotating biological contact aerator), a clarifier and, optionally, a mounting frame. The aeration basin substantially contains sludge and waste, the mixture of which is referred to as mixed liquor. The aeration basin has an inlet for receiving waste, such as an influent conduit or valve. The aerating device aerates the mixed liquor in the aeration basin.
In the clarifier, solid particles separate from the mixed liquor, resulting in recycled sludge and discharge water. Preferably, the solid particles precipitate out, leaving supernatant discharge water. The clarifier has an outlet, such as an effluent conduit or overflow weir, for discharging the supernatant. Between the clarifier and the aeration basin there is at least one opening or conduit through which either mixed liquor from the aeration basin may flow into the clarifier or sludge from the clarifier may flow into the aeration basin. Alternatively, both types of flow occur, sequentially or simultaneously. In at least one case, the flow proceeds substantially without the assistance of a pump. Most preferably, both types of flow occur through a single opening or conduit and both types of flow proceed substantially without need of a pump.
As described above, the clarifier is structurally or functionally integral with the aeration basin. The clarifier is structurally integral, for example, when the clarifier and aeration basin are partitioned from each other along their mutual boundary by a partition that creates an incomplete seal between them. The seal is incomplete where, inter alia, the partition has an opening or conduit near the floor of the aeration basin. Preferably, this opening or conduit is just large enough to allow the flow of waste into the clarifier and the flow of sludge into the aeration basin to proceed at rates sufficient to achieve the optimum amount of sludge required in the aeration basin. As such, the aeration basin and clarifier may reside in a single main tank separated only by the partition, or may be contained within a single main tank body.
In more preferred embodiments, the apparatus uses a hybrid of activated sludge and fixed film processes to treat the mixed liquor. The combination of the two technologies takes advantage of the best aspects of both types of treatment. In such cases, the aerating device preferably comprises a rotating fixed film aerator with biological contact aerator cell segments. A most preferred type of fixed film aerator, known as a xe2x80x9cBio-Wheel(trademark)xe2x80x9d (a trademark of Wastewater Technology Inc., Monterey, Va.), lacks external aerators, such as diffusers, that are present on typical fixed film aerators. Rather, the aerators are part and parcel of the Bio-Wheel(trademark). The Bio-Wheel(trademark) also includes a paddle to agitate the mixed liquor, most preferably a single paddle in a fixed position. The paddle helps force lighter aerated mixed liquor down near the opening or conduit and some of that aerated mixed liquor travels through the opening into the clarifier. The portion of the partition near the opening may be inclined, forming a partition lip, preferably inclined toward the clarifier. The waste treatment apparatus may have one clarifier or a plurality of clarifiers.
In a still more preferred embodiment, the waste treatment apparatus includes a mounting frame for mounting the aerating device within the aeration basin, wherein the mounting frame is fastened to the aeration basin at a point at or above the surface level of the mixed liquor regularly contained within the aeration basin. This is facilitated where the mounting frame has a lip that engages the top of a wall of the aeration basin. In a most preferred embodiment, the mounting frame includes a lifting means, preferably near the top, whereby the aerating device may be lifted out of the aeration basin by lifting the mounting frame. Ideally, the mounting frame is in the shape of an inverted xe2x80x9cAxe2x80x9d and a point of attachment for the aerating device is located near the apex of the mounting frame. Most preferably, the aerating device has an axle and wheel bearings that attach to the frame at the frame""s point of attachment.
The method of the invention includes the steps of directing waste into an aeration basin through an inlet; substantially containing sludge and the waste in the aeration basin, in which the sludge and waste form a mixed liquor; aerating the mixed liquor in the aeration basin with an aeration device; directing aerated mixed liquor in the aeration basin into a clarifier, removing solid particles from the mixed liquor in the clarifier to form recycled sludge and discharge water; discharging the discharge water through an outlet; and directing the recycled sludge into the aeration basin. Further, either or both the aerated mixed liquor in the aeration basin and the recycled sludge in the clarifier are directed to the clarifier and aeration basin, respectively, through an opening between the clarifier and the aeration basin. Directing the aerated mixed liquor and/or the recycled sludge involves either directing the mixed liquor from the aeration basin into the clarifier substantially without the means of a pump, directing of the recycled sludge from the clarifier into the aeration basin substantially without the means of a pump, and/or a simultaneous combination thereof.
In preferred embodiments of the method, the clarifier is structurally integral to the aeration basin in that the clarifier and aeration basin are contained within a single main tank. Also, preferably the clarifier and aeration basin are separated from each other along their mutual boundary by a partition in which the aforementioned opening is formed. More preferably, the method substantially facilitates both fixed film and activated sludge processes in the main tank. Still more preferably, the method includes the steps of mounting the aerating device on a mounting frame; placing the mounting frame and mounted aerating device into the aeration basin; and fastening the mounting frame to the aeration basin at a point at or above the surface level of the mixed liquor regularly contained within the aeration basin. This allows the aerating device to be lifted out of the aeration basin by lifting the mounting frame out of the aeration basin. The method also includes all of the preferred embodiments that were described above in reference to the apparatus.
The method and apparatus of the invention will be better understood by reference to the appended drawings and the following description.